1. Field of the Invention
This invention relates to a novel optical recording medium and the recording of information thereon. More particularly, the present invention relates to an information recording medium, preferably in the form of a disk or in tape format, suitable for use with optical recording and playback apparatus, the information layer of which comprises a naphthalocyanine chromophore. The present invention also relates to novel compounds, and in particular naphthalocyanine chromophores, which are useful in optical recording media.
2. Description of the Prior Art
Optical recording methods in which light from a laser is focused upon the surface of a recording medium with sufficient intensity to cause a detectable change in the physical characteristics of the surface material have been proposed. Among these methods is the establishment of an information pattern of pits. In such methods, the information representative pattern of pits may be formed in the surface of the recording medium by suitably controlling the intensity of the focused light in accordance with the information to be recorded while relative motion is established between the recording medium and the focused light spot.
For instance, in recent years, attention has been increasingly paid to the information recording method in which information is written in a thin film of metal or the like formed on a substrate by using a laser ray or beam. According to such a method, the information recording has been accomplished by forming holes or recesses in the metallic thin film under the action of a thermal energy beam such as a laser ray. See, e.g., U.S. Pat. No. 4,238,803.
Dyes and pigments have also been employed in information layers of recording media, often to enhance the sensitivity of the recording layers at the particular wavelength of the laser being used, which results in a much sharper recording and playback of the information.
For example, Spong, U.S. Pat. No. 4,097,895, describes a recording medium which comprises a light reflecting material, such as aluminum or gold, coated with a dye-containing light absorbing layer, such as fluorescein, which is operative with an argon laser light source. The thickness of the light absorbing layer is chosen so that the structure has minimum reflectivity. An incident light beam then creates a hole in the light absorbing layer, exposing the light reflecting layer. After recording at the wavelength of the recording light, maximum contrast between the minimum reflectance of the light absorbing layer and the reflectance of the light reflecting layer exists. In this regard, note also U.S. Pat. No. 4,219,826.
Carlson, in U.S. Pat. No. 3,475,760, discloses a system for directly recording information in a thermoplastic film as a deformation by using a high energy laser scanning beam of small diameter. It is further disclosed that the sensitivity of the films for laser film deformation recording can be enhanced by the addition of pigments or dyes which exhibit a high absorption at the laser wavelength. Erasure of the film deformation is accomplished by recording over the information to be erased using a similar laser beam but with a much smaller scan line spacing, preferably so as to provide overlap of the scan lines.
Other U.S. patents wbich disclose the use of a light absorbing dye in the recording layer include U.S. Pat. Nos. 4,412,231 and 4,446,223. The former patent discloses using a mixture of dyes having different light absorbing wavelengths so that the resulting recording layer has a light absorptivity of 80% or more at all the wavelengths in the range of from 400-900 nm. The latter patent discloses an optical information recording element comprising a support coated with a layer of an amorphous composition, which composition comprises a binder and an oxoindolizine or oxoindolizinium dye.
In a paper entitled "Single Wavelengths Optical Recording in Pure, Solvent Coated Infrared Dye Layers" by Gravesteijn, Steenbergen and van der Veen, experiments on the use of certain dyes for optical recording for digital and video applications at GaAlAs laser wavelengths are reported. The paper was presented at the Proceeding of the SPIE, "Optical Storage Media", volume 420, June 6-10, 1983. The specific dyes discussed in the paper are squarylium dyes and pentamethine dyes. It is further suggested in the paper that the solubility of the squarylium dyes in organic solvents can be greatly increased by the introduction of t-butyl groups into thiopyrylium end groups.
The use of dyes in conjunction with optical recording media comprising a styrene oligomer is disclosed in the article by Kuroiwa et al appearing in the Japanese Journal of Applied Physics, Vol. 22, No. 2, February 1983, pp. 340-343. Among the dyes and pigments discussed as being useful is a copper phthalocyanine pigment. Phase separation and incompatibility between the dyes and oligomers were noted in the article as being problems in the use of dyes for optical information media.
Lee Arnold Schechtman in his thesis Compounds, Poly(metallonaphthalocyanines) and Related Macrocyclic Compounds, August, 1983, Dept. of Chemistry, Case Western Reserve University, discloses a particular chromophore which absorbs light at the wavelength of about 770 nm, i.e., bis-tri-n-hexylsiloxysilicon naphthalocyanine. The suitability of such a chromophore for use in an optical recording medium, however, has heretofore not been suggested or explored.
S. A. Mikhalenko and E. A. Luk'yanets in "Phthalocyanines and Related Compounds II. Synthesis and Certain Properties of 2,3-naphthalocyanines", Zhurnal Obshchei Khimii, Vol. 30, No. 11, pp. 2554-2558, November, 1969, disclose certain substituted 2,3-naphthalocyanines. The suitability of such compounds for use in optical recording media, however, is not suggested therein. Note also Vogler and Kunkely, "Template Synthesis and Optical Spectra of Zinc-2,3-naphthalocyanine", Inorganica Chemica Acta, 44 (1980), L209-L210.
The recording medium, of course, is one of the key elements in any optical recording system, i.e., a system in which the information is recorded or read by light. Such system would have a usefulness in the storage of audio and video information, data processing and document processing. The commercial viability of an optical recording medium would of course depend upon such technical parameters as the sharpness in recording and playback of the information, i.e., a high signal to noise ratio, as well as the useful life of the information medium. Maintaining the sensitivity of a recording medium throughout the cycles of record-read-erase is also an important consideration.
While dyes or pigments have been employed in information storage layers of recording media due to their excellent absorption properties, the search for an improved information storage medium comprising a dye or pigment exhibiting stability and intense absorption at specified wavelengths is continuously ongoing. The sensitivity of the dye recording media often degrades due to the chemical or photolytic instability of the dye material used. Thus, the useful life of the recording medium is cut short. Furthermore, the ability of the dye to be applied in a polymer film is often a problem due to the lack of solubility in conventional solvents. Attempts to alter the dye molecule, however, often result in an undesirable change in its spectral properties.
Accordingly, it is a major object of the present invention to provide a novel recording medium which comprises a dye or pigment in the information layer.
Yet another object of the present invention is to provide a dye material for use in an information layer of an optical recording medium which exhibits excellent absorption properties.
Still another object of the present invention is to provide a novel dye material which exhibits excellent absorption properties at a wavelength ranging from about 760-850 nm.
It is still another object of the present invention to provide a dye containing recording medium which has excellent stability and can thereby provide a longer useful life.
It is yet another object of the present invention to provide a dye containing erasable recording medium which maintains its sensitivity through multiple record-read-erase cycles.
It is still another object of the present invention to provide novel chromophore compounds which are useful in optical recording media.
Yet another object of the present invention is the provision of chromophore compounds exhibiting excellent solubility characteristics so that they might readily be applied as a film onto a substrate, thereby enhancing their applicability as a recording layer in an optical recording medium.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.